Process for the preparation of vanadyl sulfate solution

ABSTRACT

A process for producing a vanadyl sulphate solution (VOSO4) comprises forming a suspension of vanadium trioxide (V2O3) in a sulphuric acid solution and contacting the V2O3 suspension with a strong oxidising agent under controlled conditions to produce the VOSO4 solution. A preferred oxidising agent is hydrogen peroxide, which is added very slowly to the V2O3 suspension due to the violent nature of the reaction.

BACKGROUND TO THE INVENTION

THIS invention relates to a process for the preparation of a vanadylsulphate solution.

It is known to produce vanadyl sulphate by dissolving vanadium pentoxidein hot dilute sulphuric acid under vigorous agitation and continuedheating with the aid of sulphur dioxide as a reducing agent.

The limited solubility of sulphur dioxide in acidic and aqueoussolutions results in the emission of sulphur dioxide from the solutionand this presents an environmental hazard. Overdosing of the solutionwith SO₂ gas results in the unwanted formation of the lower valentvanadium sulphate, namely V₂SO₄ and not vanadyl sulphate (VOSO₄).

Since the dissolution of vanadium pentoxide in sulphuric acid isendothermic heat has to be provided to drive the formation of vanadylsulphate.

There is thus always a need for a new method for the production ofvanadyl sulphate.

SUMMARY OF THE INVENTION

According to the invention a process for producing a vanadyl sulphatesolution includes the steps of:

-   (1) providing a starting material comprising vanadium trioxide    (V₂O₃);-   (2) contacting the vanadium trioxide with an appropriate volume and    concentration of a sulphuric acid solution to produce a vanadium    trioxide suspension; and-   (3) contacting the vanadium trioxide suspension with a strong    oxidising agent that is capable of raising the valency or oxidation    state of the vanadium, thereby to dissolve the vanadium trioxide in    the sulphuric acid to produce the vanadyl sulphate solution (VOSO₄).

Various strong oxidising agents including peroxides and permanganatesuch as hydrogen peroxide, sodium peroxide and potassium permanganate,for example, can be used. Hydrogen peroxide is particularly preferred asit does not introduce any impurities into the final product.

The hydrogen peroxide is typically added slowly to the vanadium trioxidesuspension due to the violent nature of the reaction.

BRIEF DESCRIPTION OF THE DRAWING

The invention will now be described in more detail, by way of exampleonly, with reference to the accompanying drawings in which:

FIG. 1 is a graph indicating the mass relationship between varyingquality V₂O₃ expressed as V₂O₅ against constant 4.5 g V₂O₅ portions in a4.0 molar sulphuric acid solution; and

FIG. 2 indicates the reduction potential in mVolt against the mass ofthe V₂O₃ used.

DESCRIPTION OF A PREFERRED EMBODIMENT

The crux of the invention is to use a strong oxidising agent to dissolvevanadium trioxide (V₂O₃), commonly referred to as Hivox, in a sulphuricacid solution to produce vanadyl sulphate (VOSO₄).

In carrying out the process, a strong oxidising agent such as a peroxideor permanganate, for example, is used to dissolve the V₂O₃ in a warmsulphuric acid solution with constant stirring. Although various strongoxidising agents such as hydrogen peroxide, sodium peroxide, potassiumpermanganate, iodine, potassium iodate, potassium bromate, bromine,ammonium persulfate, persulfates of sodium and potassium, cerium (IV)sulphate, and potassium dichromate, for example, can be used, hydrogenperoxide is preferred as it does not introduce any impurities into thefinal product.

As the quality of industrial grade Hivox ranges typically from 115 to122 percent equivalent V₂O₅, FIG. 1 can be used in order to determine anappropriate quantity of V₂O₃ for use in the process, depending on thequality of the starting material used. The required solution can beobtained by monitoring the reduction potential thereof in mVolt, asshown in FIG. 2, during the dissolution process. The start of productionof vanadyl sulphate is illustrated at the point where the graph dipssharply.

The invention will now be illustrated by way of the followingnon-limiting example.

EXAMPLE

Hydrogen peroxide was used to dissolve 3.0 grams Hivox (V₂O₃) in a warm(50° C.) 4.0 molar sulphuric acid solution with constant stirring. Thehydrogen peroxide was added dropwise as it reacted violently with thesolution. During the dissolution process the reduction potential of thesolution was continuously monitored and the addition of hydrogenperoxide stopped when the solution reached the end point at 600 mVolts.

The process proceeded according to the following formula:2V₂O₃+4H₂SO₄+H₂O₂→4VOSO₄+4H₂O+H_(2↑).

During the process, the solution first turned green, which is indicativeof the presence of V³⁺ ions, whereafter it turned blue, which isindicative of the presence of VO²⁺ ions present in the vanadyl sulphateend product.

From the above, it is evident that vanadyl sulphate can readily be madeusing Hivox (V₂O₃), which is generally more cost effective, and lesshazardous, than the conventional process using V₂O₅.

1. A process for producing a vanadyl sulphate solution including thesteps of: (1) providing a starting material comprising vanadium trioxide(V₂O₃); (2) contacting the vanadium trioxide with a sulphuric acidsolution to produce a vanadium trioxide suspension; and (3) contactingthe vanadium trioxide suspension with a strong oxidising agent, that iscapable of raising the valency or oxidation state of the vanadium,thereby to dissolve the vanadium trioxide in the sulphuric acid toproduce the vanadyl sulphate solution (VOSO₄).
 2. A process according toclaim 1, wherein the strong oxidising agent is selected from the groupconsisting of hydrogen peroxide, sodium peroxide, potassiumpermanganate, iodine, potassium iodate, potassium bromate, bromine,ammonium persulfate, persulfates of sodium and potassium, cerium (IV)sulphate, and potassium dichromate.
 3. A process according to claim 2,wherein the strong oxidising agent is hydrogen peroxide.
 4. A processaccording to claim 3, wherein the hydrogen peroxide is added dropwise tothe vanadium trioxide suspension.
 5. A process according to claim 4,wherein the addition of hydrogen peroxide is stopped when the reductionpotential of the vanadium sulphate solution reaches a predetermined endpoint.
 6. A process according to claim 5, wherein the end point is atabout 600 mVolts.